The art has long sought an inexpensive, efficient and environmentally sound way to produce polymers, particularly low molecular weight oligomers. Such oligomers have been found very useful in producing low VOC (volatile organic component) coating compositions typically used in automotive OEM (original equipment manufacturer) and refinish applications. One method of achieving low molecular weight polymers is through the use of efficient chain transfer agents, but this approach has several drawbacks. This approach incorporates the structure of the chain transfer agent into the polymer chain. This can be undesirable since that structure will have an increasing effect on the properties of the polymer as molecular weight decreases. Furthermore, the chain transfer agents commonly employed are mercaptans. These materials are expensive and have objectionable odors associated with their presence. Other common chain transfer agents are hypophosphites, bisulfites and alcohols. These also add to the cost of the process, impart functionality to the polymer, can introduce salts into the product, and may necessitate a product separation step. Another way of lowering the molecular weight of the polymers produced is by increasing the amount of initiator. This approach adds considerably to the cost of production and may result in polymer chain degradation, crosslinking, and high levels of unreacted initiator remaining in the product. In addition, high levels of initiator may also result in high levels of salt by-products in the polymer mixture, which is known to be detrimental to performance in many applications. The same is true for chain stopping agents such as sodium metabisulfite. Among the preferred free-radical initiators for aqueous polymerization is hydrogen peroxide. It is relatively inexpensive, has low toxicity, and does not produce detrimental salt by-products. However, hydrogen peroxide does not generally decompose efficiently at conventional polymerization temperatures and large amounts must normally be used to generate enough radicals to carry out a polymerization.
An attempt was made in the U.S. Pat. No. 6,046,278 to address the aforedescribed concerns by utilizing a inductively heating tubular reactor at ultra high pressures ranging from 1,000 to 5,000 pounds per square inch (psi) and temperatures ranging from 250° C. to 500° C. to polymerize a reaction mixture in 0.1 seconds to 5 minutes. However, a need still exists for a pressurized process that can safely handle exothermic polymerization of acrylic monomers.